A 7-digit phone number can be represented as \( d_1 d_2 d_3 d_4 d_5 d_6 d_7 \), where \( d_1 \) is the first digit and the remaining digits \( d_2, d_3, d_4, d_5, d_6, d_7 \) are the subsequent digits.
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For the first digit \( d_1 \):
- It cannot be 0 and can be any digit from 1 to 9.
- Therefore, there are 9 possible choices for \( d_1 \) (1 through 9).
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For each of the remaining digits \( d_2, d_3, d_4, d_5, d_6, d_7 \):
- Each can be any digit from 0 to 9.
- Hence, each of these digits has 10 possible choices.
Now, we can calculate the total number of 7-digit phone numbers by multiplying the number of choices for each digit:
\[ \text{Total numbers} = (\text{choices for } d_1) \times (\text{choices for } d_2) \times (\text{choices for } d_3) \times (\text{choices for } d_4) \times (\text{choices for } d_5) \times (\text{choices for } d_6) \times (\text{choices for } d_7 \]
Substituting in the values:
\[ \text{Total numbers} = 9 \times 10 \times 10 \times 10 \times 10 \times 10 \times 10 \]
This simplifies to:
\[ \text{Total numbers} = 9 \times 10^6 \]
Calculating this gives:
\[ \text{Total numbers} = 9,000,000 \]
Therefore, the total number of 7-digit phone numbers possible, under the given restrictions, is \( \boxed{9000000} \).
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